Predatory behavior of Delphastus pusillus in relation to the phenotypic plasticity of Bemisia tabaci nymphs
1999
Guershon, M. | Gerling, D.
Phenotypic plasticity in Bemisia tabaci is expressed, among others, through the degree of nymphal setosity. We tested the hypothesis that the setose phenotype of nymphs can act as a defense mechanism against the predatory coccinellid Delphastus pusillus. Since it has been shown that the relative number of each phenotype is directly correlated with the tomentosity level of the host leaf, our study included characterization of D. pusillus predatory activity when exposed to the different nymphs upon two different leaf types: glabrous and tomentose. Leaf trichomes were found responsible for differences in durations of observed events, their frequency and transitions between events, leading to a break in the predatory sequence regularly found on glabrous leaves. However, despite this break, observational data and functional response tests showed no differences in prey consumption when the predator was exposed to each prey type separately. This is explained by a particular foraging behavior displayed by D. pusillus on tomentose leaves that included walking upon leaf trichomes while performing a vertical introduction of the head between the trichomes, thus reaching the leaf surface. Differences in handling times between the nymph phenotypes were recorded during direct observations of patch time allocation, but these did not result in significant differences in the number of prey eaten. Moreover, our estimates of handling time, calculated with a type II functional response equation, also failed to show these differences. However, foraging predators were more prone to discover smooth nymphs than setose nymphs when the former were offered on tomentose leaves. The significance of these findings in the context of predator-prey-plant interactions is discussed.
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